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Fix description of stack! in quick start #1156

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Fix description of stack! in quick start #1156

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71 changes: 50 additions & 21 deletions README-quick-start.md
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Expand Up @@ -352,39 +352,68 @@ c =
[4.0, 9.0]], shape=[6, 2], strides=[2, 1], layout=C (0x1), const ndim=2
```

### Stacking together different arrays
### Stacking/concatenating together different arrays

The `stack!` and `concatenate!` macros are helpful for stacking/concatenating
arrays. The `stack!` macro stacks arrays along a new axis, while the
`concatenate!` macro concatenates arrays along an existing axis:

Macro `stack!` is helpful for stacking arrays:
```rust
use ndarray::prelude::*;
use ndarray::{Array, Axis, stack};
use ndarray::{concatenate, stack, Axis};

fn main() {

let a = array![
[9., 7.],
[5., 2.]];

[3., 7., 8.],
[5., 2., 4.],
];

let b = array![
[1., 9.],
[5., 1.]];

println!("a vstack b = \n{:?}\n", stack![Axis(0), a, b]);

println!("a hstack b = \n{:?}\n", stack![Axis(1), a, b]);
[1., 9., 0.],
[5., 4., 1.],
];

println!("stack, axis 0:\n{:?}\n", stack![Axis(0), a, b]);
println!("stack, axis 1:\n{:?}\n", stack![Axis(1), a, b]);
println!("stack, axis 2:\n{:?}\n", stack![Axis(2), a, b]);
println!("concatenate, axis 0:\n{:?}\n", concatenate![Axis(0), a, b]);
println!("concatenate, axis 1:\n{:?}\n", concatenate![Axis(1), a, b]);
}
```
The output is:
```
a vstack b =
[[9.0, 7.0],
[5.0, 2.0],
[1.0, 9.0],
[5.0, 1.0]], shape=[4, 2], strides=[2, 1], layout=C (0x1), const ndim=2
stack, axis 0:
[[[3.0, 7.0, 8.0],
[5.0, 2.0, 4.0]],

[[1.0, 9.0, 0.0],
[5.0, 4.0, 1.0]]], shape=[2, 2, 3], strides=[6, 3, 1], layout=Cc (0x5), const ndim=3

stack, axis 1:
[[[3.0, 7.0, 8.0],
[1.0, 9.0, 0.0]],

[[5.0, 2.0, 4.0],
[5.0, 4.0, 1.0]]], shape=[2, 2, 3], strides=[3, 6, 1], layout=c (0x4), const ndim=3

stack, axis 2:
[[[3.0, 1.0],
[7.0, 9.0],
[8.0, 0.0]],

[[5.0, 5.0],
[2.0, 4.0],
[4.0, 1.0]]], shape=[2, 3, 2], strides=[1, 2, 6], layout=Ff (0xa), const ndim=3

concatenate, axis 0:
[[3.0, 7.0, 8.0],
[5.0, 2.0, 4.0],
[1.0, 9.0, 0.0],
[5.0, 4.0, 1.0]], shape=[4, 3], strides=[3, 1], layout=Cc (0x5), const ndim=2

a hstack b =
[[9.0, 7.0, 1.0, 9.0],
[5.0, 2.0, 5.0, 1.0]], shape=[2, 4], strides=[4, 1], layout=C (0x1), const ndim=2
concatenate, axis 1:
[[3.0, 7.0, 8.0, 1.0, 9.0, 0.0],
[5.0, 2.0, 4.0, 5.0, 4.0, 1.0]], shape=[2, 6], strides=[1, 2], layout=Ff (0xa), const ndim=2
```

### Splitting one array into several smaller ones
Expand Down